Keying



April 19, 1938. R. BRUCKNER ET AL ,114,332

KEYING Original Filed Jan. 8, 1934 VTORS 3/04/71? BBUC/f/VEH y I900 LF 60572. EH

' ATTORNEY Patented Apr. 19, 1938 UNITED STATES FFlE PATENT KEYING Application January 8, Renewed October 21,

uary 9, 1933 8 Claims.

This invention relates to a method of and a circuit arrangement for the simultaneous keying of a self-excited and a separately-excited stage of a valve transmitter.

Telegraphic transmitters which by keying shocksresulting from hard thumping of the key may cause serious disturbances especially in receivers located at close distances, should be keyed gently and smoothly. Now, if such a transmitter including one or more stages is keyed gently in a separately-excited stage, but not in the oscillation generator of the transmitter it is found that the continuously oscillating generator produces waves which become troublesome. Upon the keying signals is superposed a permanent tone when heterodyne reception is used which tends to blur the difference between dash and space or intervals. Inasmuch as in most instances, the frequency of the oscillation generator of the transmitter differs during spaces from that during a dash, it may happen that the receiving station is adjusted to space signals with the result that negative signals are received.

In order to prevent this from happening the 7 generator of transmitter is keyed as well as the amplifier or repeater or multiplier stages. However, because of the break regions it is not possible to key it conjointly and simultaneously with the main transmitter inasmuch as upon breaking oil or resuming it would also cause shocks and undesired signals in the excited transmitter amplifier stages or repeaters. For this reason recourse has been had to circuit arrangements comprising a plurality of relays in which the generator of the transmitter is disconnected only when the fall of signal in the transmitter amplifier and repeater stages has been completed; moreover, the generator of the transmitter is re-connected before the amplifier becomes operative.

Now, the present invention dispenses with the use of a plurality of relays and with the corresponding complicated relay and retarder circuit means. In our invention the desired end, namely, gentle keying of a separately excited transmitter stage or stages and keying of the oscillation generator is accomplished in such a manner that the generator becomes disconnected or inoperative only after completion of the decay of the wave in the amplifier and resumes operation prior to the building-up in operativeness of said amplifier. In our invention this is accomplished by the aid of suitable circuit arrangements comprising electric retarder means and a single key or a single standard keying relay. The principle underlying the invention is as follows:

1934, Serial No. 705,681.

In Germany Jan- The grid blocking voltages of the keyed separately-excited amplifier or repeater stages and the generator stage are derived from a joint voltage source by way of retarding means, the ratio between the used and the least necessary blocking voltage being chosen lower for the exciting stage than for the separately excited stage.

The novel features of our invention have been pointed out with particularity in the claims at the end of the specification. Our method of keying will be better understood from the following description thereof and therefrom when read in connection with the drawing in which Figures 1 to 5 inclusive show circuit diagrams which include the essential elements for keying the generator and. a stage of the transmitter amplifier.

The idea upon which this invention is predicated shall be explained in more detail by reference to the exemplified embodiment thereof shown in Figure l of the drawing. i denotes the tube of the exciting stage or initial generator, and 2 that of a separately excited stage which may be an amplifier; 3 and 4 denote grid coupling coils, 5 and 6 grid blocking condensers, l and 8 grid direct current resistances; H3 is a keying relay which short-circuits potentiometer 9 at the rythin of the Morse-code. With the relay being closed, the grid biasing voltage generator I 2 is short-circuited upon the resistance H. The grid direct current of the exciting or generator stage flows by way of parts BA and CA of the potentiometer 9 and the resistance 1 (which optionally may be dispensed with) and results in the biasing voltage for upper dash. In the separately excited stage the grid direct current flows through the key relay Ill and produces across the terminals of resistance 8 the biasing voltage for the grid of tube 2 to amplify the upper dash. If, then, the keying relay ill be opened, the capacity 6 will be charged by way of resistances 8 and H so that a negative blocking voltage is applied to the grid of 2. These currents in addition apply a suitable biasing voltage to the grid of the pilot tube 1 by way of the potentiometer Q and resistance l and a charging potential of the condenser 5. By suitably choosing the resistances 8, i, i i, ii, and of the capacities 6 and 5 the rise and fall of the plate alternating current of both the separately excited and the self-excited tubes is influenced. By suitable adjustment of the sliding contact A of the potentiometer 9 conditions can be made so that the tube 5 will be blocked v only after blocking'has been efiected in tube 2,

and that tube I will be unblocked before tube 2 has been unblocked. In practice, of course, care iii) must be taken so as to provide proper choking, especially in so far as the keying relay I0 is concerned, in order that the switching spark may not give rise to audio frequency disturbances.

Another exemplified embodiment of the invention is indicated in Figure 2. The plate voltage and the grid biasing voltage are derived from a joint voltage source It, the voltage being divided by the resistances 9 and I5. In series with the keying relay I0 generally is a resistance l3. Some of the circuit elements l6, ll, l8, l9, under certain circumstances, may be dispensed with.

If the form of the building up and decay of the signal should not be perfectly satisfactory it is possible by the insertion of choke-coils to insure extensive changes in the shape of the signals. Two embodiments are shown in Figures 3 and 4. In the case of Figure 3 there is disposed in series with resistance 8 a choke-coil with a parallel resistance 2|; in Figure 4, a choke-coil 22 with parallel resistance 23 is connected between capacities 6 and 24.

In order that the duration of the rise and fall of the signals may be varied independently of one another, a rectifier is connected in parallel relation to some of the elements so that these elements become operative either only during the rise or only during the fall of the signals.

One important embodiment is shown in Figure 5. In parallel relation to the capacity 6 is a branch with condenser 25 and a resistance 26 in series, 25 being bridged or shunted by a device 21, for instance, a dry rectifier. In the exemplified embodiment here shown the rectifier is so connected that it will be permeable or conductive in the direction of the arrow, that is, upon discharge of the condenser. Then, during the rise of the signal, the capacity 6 will be increased by the capacity 25 and thus also the time-constant and the length of the rise is increased, whereas during the fall of the signal, if

capacities 8 and 25 and the resistance 26 are suitably dimensioned, it is initially only the capacity 6 and a smaller time-constant that become operative.

Having thus described our invention and the operation thereof, what we claim is:

1. A transmitter comprising a thermionic generator tube, a thermionic amplifier tube connected therewith, each of said tubes having a grid and a cathode, means for keying said generator and said amplifier comprising a source of direct current, a resistance in shunt therewith, a connection between a point intermediate the terminals of said resistance and the grid of said generator tube, a connection between the oathodes of said tubes and one terminal of said source, a connection between another point on said resistance and the grid of said amplifier tube, a resistance and a rectifier in parallel in shunt to said first named resistance, and a key in shunt with said resistance.

2. A transmitter comprising a thermionic oscillation generator tube, a thermionic amplifier tube connected therewith to amplify the oscillations generated by said generator tube, each of said tubes having a control grid and a cathode, means for keying said generator tube and said amplifier tube comprising a source of direct current potential, a resistance and a condenser connected in means connecting the control grid of the other of said tubes to a different point on said first named resistance, a reactance and a resistance in parallel in one of said last named connections and a circuit connecting the cathodes of both of said tubes to a third point on said first named resistance.

3. An arrangement as recited in claim 2 in which a condenser is connected between each of the terminals of said parallel reactance and resistance and the cathode of one of said tubes.

l. A transmitter comprising a thermionic oscillation generator tube, a thermionic amplifier tube connected therewith to amplify the oscillations generated by said generator tube, each of said tubes having a control grid and a cathode, means for keying said generator tube and said amplifier tube comprising a source of direct current potential, a resistance and a condenser connected in parallel with said source of direct current potential, a key connected in parallel with said source of direct current potential, resistive means connecting the control grid of one of said tubes to a point on said first named resistance, resistive means connecting the control grid of the other i of said tubes to a different point on said first named resistance, a condenser connected between the control grid and cathode of said amplifier tube, a rectifier connected in parallel with said last named condenser and a circuit connecting the cathodes of both of said tubes to a third point on said first named resistance.

5. In a telegraph transmitter, a transmitter tube having input electrodes and having output electrodes connected in a transmitter circuit, an

exciting tube having output electrodes coupled to the input electrodes of said transmitter tube, a source of direct current, a direct current impedance connected with said source of direct current, a key connected with said impedance to control the potential drop produced across said impedance by said source of direct current, and means connecting points on said impedance to said tube electrodes for rendering said exciting tube operative and then rendering said transmitter tube operative each time said key is placed in marking position and for rendering said exciting tube inoperative after rendering said transmitting tube inoperative each time said key is placed in the spacing position.

6. A telegraph transmitter as recited in claim 5 wherein said means includes additional direct current impedances in series in said network and current storing devices in shunt to said direct current .network.

7. In a telegraph transmitter, a transmitter tube having input electrodes and having output electrodes connected in a transmitting circuit, an exciting tube having output electrodes coupled to the input electrodes of said transmitter tube, a source of direct current potential, an impedance connected with said direct current source, a key connected with said direct current source and impedance for controlling the potential drop produced in the impedance by said direct current source, a direct current network, including said impedance and key, connecting said source of direct current potential to the electrodes of said tubes to control the operativeness thereotby controlling the direct current potential supplied by said source to said electrodes of said tubes, and additional impedance means in said connections between said tube electrodes and said network cooperating with said first impedance and key for rendering said 75 exciting tube operative and then rendering said transmitter tube operative each time said key is in marking position and for rendering said exciting tube inoperative after rendering said transmitting tube inoperative each time said key is placed in the spacing position.

8. A telegraph system as recited in claim 7 wherein said network includes current storing devices in shunt to said network and additional direct current impedances in series in said network.

RICHARD BRUCKNER.

RUDOLF GiiRTLER. 

